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QUDOS - the brilliant new amplifier boards from Avondale

Yes, it's a bit of a hybrid of NC200 and NC220 values I suspect (e.g. R2) - I think it was one of Les's early boards. The diagram is what Les sent me just before he went away to help be debug a couple of issues with the board.

Am awaiting the Maestro's word though before I start with the soldering iron.
 
Chris, looks good. What did you use to cut through the heatsink? I have some here I need to cut down and need to see which of the existing power tools in the garage is going to be capable...
 
Here's something else to throw into the equation - an old thread discussing regulating the front end of the NCC200. When I had my amp apart I realised that I had done this way back when - as well as replacing the standard 0R22 resistors with some Meggit thick film resistors.

I don't have room in my case for full on regulator boards, so am thinking I may go this way again with the NCC220s....

NCC_frontend_reg.jpg


...or are there better options nowadays?

Insteresting looking back at that thread, as Les recommends removing the 39pF cap (C13) as a nice tweak - and lo and behold, it is not present on the Qudos boards.
 
When I was off work and couldn’t afford the VBEs I copied the onboard regulation from the HackerNap. It’s only a handful of parts which fit on a small piece of vero. Later Les sold me some small circuit boards with the components that do the same. I still have some somewhere. I’ll dig them out if you’re interested.
James, a bandsaw is useful for cutting those heat sinks in half or failing that I’d put a fine blade in the table saw.
 
I am ordering some resistors to build a pair of Qudos/220 boards, I have almost no knowledge of electronics and am finding it difficult to choose the 4 special resistors at R9, R12, R14 and R15 on the circuit diagram at post 370.

The values are 2.7K, 1K, 24K and 27K and Les recomends " should be high precision metal film ie RC55 or better".

Any suggestions regarding the what and where from for a chronically uninformed first time builder.

Thanks in advance Bill.
 
Richard - nice diagram, and that will work fine.

Do add a protection diode from the junction of R1-R2 in each case, reverse-biased back to the input pin. At higher voltages it will stop the charge on the 10uF bypass cap killing the reg from injection into Vadj if the input supply falls faster than c1 can discharge (possible with a large value of R2). NB LM337s are really quite sensitive to this, IME.

I'd also recomend to add a 1w zener diode, say 12 or 15v, reverse-biased from input pin to output. As switch-on this can avalanche and ensure the 3-pin reg is never exposed to more than 12-15 v across it (datasheet limit is 37v of course) - but once the reg is running it is totally out of circuit. With output cap at low voltage/ charging at switch-on you might get >35v transients across the reg (NB this trick becomes essential if you go much larger than 10uF.) It also acts as a regular forward bised diode at switch-off , so teh reg cannot endup ,again, reverse-biased.

Both my SOP for using 3-pin regs at higher voltages, and cheap protection. You can use 317s well over 300v with such measures ;)
 
Bill Colledge said:
I am ordering some resistors to build a pair of Qudos/220 boards, I have almost no knowledge of electronics and am finding it difficult to choose the 4 special resistors at R9, R12, R14 and R15 on the circuit diagram at post 370.

The values are 2.7K, 1K, 24K and 27K and Les recomends " should be high precision metal film ie RC55 or better".

Any suggestions regarding the what and where from for a chronically uninformed first time builder.

Thanks in advance Bill.
Click to expand...

Bill I probably have a set of those resistors, Dale RN60/55s which are good quality. I'll see if I can make a complete set up and send them off to you. I assume you are in the EU?

Farnell/CPC/RS used to stock RC55s. Not sure what they have these days.
 
Bill Colledge said:
I am ordering some resistors to build a pair of Qudos/220 boards, I have almost no knowledge of electronics and am finding it difficult to choose the 4 special resistors at R9, R12, R14 and R15 on the circuit diagram at post 370.

The values are 2.7K, 1K, 24K and 27K and Les recomends " should be high precision metal film ie RC55 or better".

Any suggestions regarding the what and where from for a chronically uninformed first time builder.

Thanks in advance Bill.
Click to expand...


I see the values here Bill... ignore my PM
 
Bill Colledge said:
I am ordering some resistors to build a pair of Qudos/220 boards, I have almost no knowledge of electronics and am finding it difficult to choose the 4 special resistors at R9, R12, R14 and R15 on the circuit diagram at post 370.

The values are 2.7K, 1K, 24K and 27K and Les recommends " should be high precision metal film ie RC55 or better".

Any suggestions regarding the what and where from for a chronically uninformed first time builder.

Thanks in advance Bill.
Click to expand...

These RC55Y resistors from Farnell will be fine:

24K3 part number 9501304
2K74 part number 9501606
1K0 part number 9500723
26K7 part number 9501380

They cost just over £2 each including VAT. It's not necessary to have exactly 2K7, 1K, 24K and 27K, it's more to do with the quality and tolerances of the components.

HTH
 
Chops54 said:
When I was off work and couldn’t afford the VBEs I copied the onboard regulation from the HackerNap. It’s only a handful of parts which fit on a small piece of vero. Later Les sold me some small circuit boards with the components that do the same. I still have some somewhere. I’ll dig them out if you’re interested.
Click to expand...

Yes, that would be nifty - thanks!

R
 
Bill Colledge said:
I am ordering some resistors to build a pair of Qudos/220 boards, I have almost no knowledge of electronics and am finding it difficult to choose the 4 special resistors at R9, R12, R14 and R15 on the circuit diagram at post 370.

The values are 2.7K, 1K, 24K and 27K and Les recommends " should be high precision metal film ie RC55 or better".

Any suggestions regarding the what and where from for a chronically uninformed first time builder.

Thanks in advance Bill.
Click to expand...

Thanks for the advice/ help regarding the resistors Chaps.

Bill
 
Sorry for the repost, but I'd really like to know the answer to this:

BC546s (TR1, 2, and 3) come in 3 hfe ranges (A=110-220, B=200-450, and C=420-800). What's the recommendation for which range to use?

Thanks!
Flash
 
RichardH said:
This is the most recent version of the circuit that I have

avondale_qudos_circuit_diag.gif


...and their location on the board
avondale-qudos-board-labelled2.jpg
Click to expand...
I am leaving Les to build mine as I need 2 pairs in my m2 monos !!
Hope to have them installed after a road trip up to chesterfield at the end of the month
Can’t wait:):)
Tony
 
martin clark said:
Richard - nice diagram, and that will work fine.

Do add a protection diode from the junction of R1-R2 in each case, reverse-biased back to the input pin. At higher voltages it will stop the charge on the 10uF bypass cap killing the reg from injection into Vadj if the input supply falls faster than c1 can discharge (possible with a large value of R2). NB LM337s are really quite sensitive to this, IME.

I'd also recomend to add a 1w zener diode, say 12 or 15v, reverse-biased from input pin to output. As switch-on this can avalanche and ensure the 3-pin reg is never exposed to more than 12-15 v across it (datasheet limit is 37v of course) - but once the reg is running it is totally out of circuit. With output cap at low voltage/ charging at switch-on you might get >35v transients across the reg (NB this trick becomes essential if you go much larger than 10uF.) It also acts as a regular forward bised diode at switch-off , so teh reg cannot endup ,again, reverse-biased.

Both my SOP for using 3-pin regs at higher voltages, and cheap protection. You can use 317s well over 300v with such measures ;)
Click to expand...

Hi Martin, could you post a schematic / diagram like Richard's above (post ~384) as I am a relative novice but can follow a circuit diagram much more easily than textual instructions.
Thanks Graham
 
Richard dug out the diagram I had in mind from the datasheet: this is the diagram I had in mind, even if I probably owrded it wrong !

D1 can be a a regular diode, or a 12-15v zener as I suggested ( because that still works as a protection diode at switch-off, but protects the reg against excess voltage drop at turn-on); D2 - any convenient diode. It's the use of D2 that becomes essential at higher voltages and espesially if you increase the capacity of C1.

NB - you really should ensure there is a cap to 0v right at the input of the three-pin reg, 10uF or more. In an application like the one we are discussing here, putting a small value resistor in series from the amp rail before that would be an excellent idea - say 10ohms/100uF to 0v. Or feed the reg from existing RC in the rails on LesW's amp boards.

317protect.png
 
Martin, I will message you an amended diagram to get the once-over before posting publicly, so we don't end up with incorrect stuff out there.
 
OK, try this for size:

NCC_frontend_reg-v3.jpg


Feel free to shoot it down in flames (metaphorical, not literal I hope!).

I would suggest anyone fancying trying all this gubbins should get the boards up and running in their standard format first, though!

[EDITED TO CORRECT THE DIAGRAM]
 
Last edited:
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